Hollow cathode discharge lamp for generating radiation characteristic of the gas fill within the envelope

ABSTRACT

A hollow cathode lamp for generating an intense small light spot representative of the gas fill within the envelope and means associated with a baffle member provided between the hollow cathode and the anode of the lamp to permit low starting voltages.

United States Patent Yamasaki Dec. 17, 1974 HOLLOW CATHODE DISCHARGE LAMP [56] References Cited FOR GENERATING RADIATION UNITED STATES PATENTS CHARACTERISTIC OF THE GAS FILL 1,751,606 3/1930 Schroter 313/197 x WITHIN TH ENVELOP 1,917,739 7/1933 Schroter 313/197 x 1,999,649 4/1935 Brett 3l3/l93 [75 1 Inventor g g Yamasak" Horseheads 3,406,308 l0/l968 Yamasuki 313/2119 x [73] Assignee: Westinghouse Electric Corporation. Primary Emmincr-Puh'ner C. DeMcn Plttsburgh, Attorney, Agent, or Firm-W. C. Sutclill [22] Filed: July 28, 1970 [21] Appl. No.: 58,790 [57] ABSTRACT A hollow cathode lamp for generatmg an mtense small light spot representative of the gas fill within the enve- U-S- lope and means associated a baffle member pro- Clvided between the hollow athode and the anode of [58] Field of Search 313/209, 1933;315:0846; h l to it 1 w starting voltages.

1 Claim, 4 Drawing Figures PATEMTEDH 71974 7 3,855,491

. POWER SUPPLY l FIG.3T

44 POWER 5 SPECTRAL LINES PRODUCED BY CATHODE MATERIAL WITH BAFFLING HYDROGEN CONTI NUUM FIG.4

RELATIVE INTENSITY WITHOUT BAFFLING WAVE LENGTH-- WITNESSES INVENTOR George KYumosok:

HOLLOW CATHODE DISCHARGE LAMP FOR GENERATING RADIATION CIIARACTERISTIC OF THE GAS FILL WITHIN THE ENVELOPE BACKGROUND OF THE INVENTION Hollow cathode lamps have been known for a considerable length of time as represented in US. Pat. No. 1,900,578 which was issued to D. Moore, Mar. 7, 1933. The lamp described therein is primarily concerned with emission of light characteristic of the gas fill. More recently, a considerable amount of work has been done to provide hollow cathode lamps which emit spectral lines characteristic of the material of the cathode. Such a device is described in US. Pat. No. 3,264,51 1, issued to G. K. Yamasaki on Aug. 2, 1966. US. Pat. No. 3,264,511 is concerned with improving the efficiency and the intensity of the light source so as to give off spectral lines representative of the cathode material. More specifically, US. Pat. No. 3,264,511 directed to confining the electrical discharge to within the hollow portion of the cathode so as to maximize the output from the device. US. Pat. No. 1,900,578 is generally directed to a hollow cathode structure for emitting a broad band type radiation primarily representative of the gas fill.

Most presently available light sources capable of emission of radiation characteristic of a gas such as hydrogen require a filament heating power supply as well as a power supply for producing the discharge.

SUMMARY OF THE INVENTION In accordance with the present invention, a hollow cathode lamp is provided to generate radiations characteristic of a gas fill such as hydrogen. The device includes an envelope having a gas fill with a hollow cathode and an anode. A baffle electrode is provided between the cathode and anode. The baffle electrode includes an aperture smaller than the crater in the hollow cathode to constrict the gas discharge into a small intense light spot and restrict the passage of spectral light generated within the crater due to the cathode material. The baffle electrode may also be connected to desired potential to lower the starting voltage of the device. The device does not require any heating current for the cathode.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiment, exemplary of the invention, shown in the accompanying DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, there is shown a hollow cathode discharge device in accordance with the present invention. This device includes an envelope 10 of a suitable material such as glass, having an enlarged tubular portion 12 and a smaller tubular portion 14 which are interconnected by a transition portion 13. The tubular portion 14 is sealed off at one end by a window 16. The window 16 is of a suitable material for efficiently transmitting wave lengths of radiation produced by the device. For example, if the device includes a hydrogen gas fill and the desired radiation is from 1,90OA to 4,000A, quartz may be used as the material for the window 16. The tubular portion 12 is sealed off by a button stem header 18 having a suitable tip off exhaust tube 20 in a manner well known in the art.

Supported by the header 18 and disposed within the tubular portion 12, there is positioned a cathode 22 which is of any desired electrical conductivity material. For example, the cathode 20 may be of nickel material with a good electron emission coating such as on the hollow portion of the cathode 22. The cathode 22 may be fabricated from any metal or alloy provided it is capable of withstanding a temperature over about 200 to 300C without melting or excessive evaporation. The cathode 22 is substantially cylindrical in shape and has a centrally extending bore or crater 24 extending from the end of the cathode 22 facing the window 16 into the cathode 22 for a considerable distance. In one specific example, the diameter of the cathode 22 is threeeighths inch and the bore 24 has a'diameter of fivesixteenths inch and a depth of one-half inch. The cathode 22 is supported by a conductive lead member 26, of a suitable electrically conductive material such as nickel which is affixed to the cathode 22 and extends through the header 18 to the exterior of the envelope 10. The lead 26 not only serves to support the cathode 22 within the envelope 10 but also serves to provide it with an electrical potential as will be explained later.

An anode 28, which is shown in the fonn of an annular metallic member, is positioned between the cathode 22 and the window 16. The aperture in the anode 28 has a diameter of about one-eighth inch. The anode 28 is of a suitable electrically conductive material such as tantalum, nickel, or any other conductive material and is supported, in the illustrated embodiment, by means of a support rod 30 of a suitable electrically conductive material such as nickel with an electrical conductive lead 31 extending from the support rod 30 to the anode 28. In addition the anode 28 is supported within an annular spacer member 32 of a suitable insulating material such as mica with an aperture provided in the annular spacer 32 for the anode 28 as well as an aperture therein for the electrode lead 30. The support lead 30 extends through the header 18 to the exterior of the envelope 10 and serves as a means by which a potential may be applied to the anode 28.

A baffle electrode 40 is provided between the anode 28 and the cathode 22. The baffle electrode 40 is also annular in shape having an aperture of a diameter of about 0.050 inch. The baffle electrode 40 may be of any suitable electrical conductive material having a thickness of about 0.020 inch. The material for the baffle electrode 40 may be of any high melting point metal such as iron, steel, tungsten, or nickel or be of an insulating material such as a ceramic on which an electrically conductive surface has been applied. The materials within the envelope should be selected so as to be effectively non-reactive to the fill gas so that they will not absorb or clean up any of the gas fill. The baffle electrode 40 may be supported in a similar manner as the anode 28. An electrode support lead 42 of a suitable electrical conductive material such as nickel is provided. This support lead 42 extends through the header 18 to the exterior of the tube and serves for applying a potential to the baffle electrode 40. In addition, an insulating spacer 44 is provided with a central opening in which the baffle electrode 40 is positioned and a conductive lead 46 of a suitable material such as nickel extends from the baffle electrode 40 to the support lead 42. The support lead 42 extends through apertures provided within the spacers 32 and 44.

In addition to the spacers 32 and 44, an additional spacer 48 is provided which has a central aperture which surrounds the cathode 22 and also has apertures through which the support leads 30 and 42 extend. A mica spacer 50 may also be provided between the spacer 44 and the cathode 22. A spacer 52 may be provided between the spacer 32 and the spacer 44. A spacer 54 may be also provided on the upper surface of the spacer 32 and between the spacer 32 and the window 16. It is obvious that a lesser or greater number of spacers may be utilized. The sandwich like structure is supported by the support rods 30 and 42. A ceramic insulating sleeve 60 is provided about the support lead 30 and extends from the header 18 to the spacer 48. A similar sleeve 62 is provided for the support lead 42 and extends from the header 18 to the spacer 48. In addition, a sleeve 64 is provided about the support lead 30 between the spacer 48 and the spacer 50. A similar sleeve 66 is provided about the support lead 42 and between the spacer 48 and the spacer 50. Tabs 70 may be provided near the ends of the support leads 30 and 42 as illustrated for securing the entire assembly in a unitary structure.

The structure illustrated provides means of preventing unwanted electrical discharge from occurring between the anode 28 or the baffle electrode 40 and the outer surface of the cathode 22 or to the associated support members therefor. It is also possible to provide an insulating sleeve about the cathode 22 to at least partially suppress a discharge between the anode 28 or baffle electrode 40 and the outer surface of the cathode 22.

In FIG. 2 there is illustrated a possible electrical connection to the device shown in FIG. 1. A power supply 80 of suitable DC potential such as about 500 volts is connected with the negative terminal connected to the cathode 22 and the positive terminal connected to the anode 28. In addition, the positive terminal of the power supply 80 is connected through a resistor 82 to the baffle electrode. The resistor 82 may be of a value of about 30,000 ohms. It would be advantageous if the value of the resistor is selected so that the cathode to baffle electrode current would be less than percent of the total device current because most of the current drawn by the baffle contribute only slightly to spectral output.

A hydrogen till 90 is provided within the envelope 10. With a hydrogen fill of 3.5 millimeters of mercury the starting voltage with'the system as shown in FIG. 2 was 330 volts and with a hydrogen fill pressure of 12 millimeters of mercury the starting potential was 390 volts. With the baffle electrode disconnected from the power supply and at floating potential the starting potential with regard to the 3.5 millimeters of fill was 450 volts and with 12 millimeters of mercury was 600 volts. It is therefore obvious with the connections indicated that there was a substantial reduction in the starting potential by the system illustrated in FIG. I.

In FIG. 3 another possible system is indicated wherein a switching member 84 may be provided for momentarily connecting the baffle electrode 40 to the positive terminal of the power supply either directly or through a resistor. It is also possible to start the device by momentarily touching the baffle lead to the anode and then removing after the discharge has been struck. This momentary triggering may be accomplished manually or with any suitable switching means such as an electromechanical device such as mercury or a thermal couple switch within or external to the device. In the case of the direct contact to the anode of the power supply the starting potential may be of about 400 V.

In FIG. 4 there is illustrated by curve 92' the spectral emission from a device of a standard hollow cathode without baffling. Curve 94 indicates the emission from a device in accordance with this invention. Curve 94 illustrates the suppression of spectral emission due to the cathode and the enhanced intensity of the device.

Another embodiment would be to place the starter wire or electrode on the cathode side of the baffle. The baffle may now be made of a conductive or of an insulating material, and require no electrical connections because the starter wire will now take over electrical functions of the baffle.

I claim as my invention:

1. A hollow cathode light source comprising an envelope, said envelope including an anode and a cathode disposed in spaced relationship for maintaining an electron discharge therebetween, said cathode having a hollow portion therein and made of a material having the property of establishing an electron discharge between said cathode and said anode, a baffle electrode positioned between said cathode and said anode and having an aperture therein of a smaller diameter than the aperture in said hollow cathode, said envelope containing hydrogen gas which is ionizable, and radiation characteristic of the hydrogen is generated and passed through the aperture in said baffle electrode in response to an electron discharge between said cathode and anode, the aperture in said baffle electrode being substantially smaller than the aperture in said cathode to restrict the passage of light generated within said hollow portion due to material of said cathode. 

1. A hollow cathode light source comprising an envelope, said envelope including an anode and a cathode disposed in spaced relationship for maintaining an electron discharge therebetween, said cathode having a hollow portion therein and made of a material having the property of establishing an electron discharge between said cathode and said anode, a baffle electrode positioned between said cathode and said anode and having an aperture therein of a smaller diameter than the aperture in said hollow cathode, said envelope containing hydrogen gas which is ionizable, and radiation characteristic of the hydrogen is generated and passed through the aperture in said baffle electrode in response to an electron discharge between said cathode and anode, the aperture in said baffle electrode being substantially smaller than the aperture in said cathode to restrict the passage of light generated within said hollow portion due to material of said cathode. 